1. Field of the Invention
The present invention relates to video-tape recording and reproducing apparatus, and more particularly to video-tape recording and reproducing apparatus in which multi-channel transformer signals are obtained from field signals by band limiting using the Hadamard Transformation System or the Time Sharing System, and which can eliminate noise caused by tape travel irregularity (unbalanced), etc., where recording and reproduction of the multi-channel transformer signals is achieved using a fixed multi-channel head.
2. Description of Prior Art
It is generally accepted that, compared with other video-tape recording and reproducing systems, such as the helical scan system, the fixed multi-channel head system is more susceptible to the effects of tape travel jitter. This is particularly so where there is a high frequency component (over several hundred Hertz) in the frequency component of the tape travel jitter. Additionally, because of the special differential characteristics of magnetic head recording and reproduction, the recording and reproduction of direct current component, which the transformer signal includes, is difficult. So, generally speaking, the transformer signal is used to frequency modulate the carrier wave, and the frequency modulated carrier wave can be recorded and reproduced. However, FM modulation and demodulation produces differential characteristics in the carrier wave phase variations.
Therefore, the jitter high frequency component can adversely affect the signal level of the demodulation signal (hereinafter called the AM component), and the jitter low frequency component can adversely affect the time base variation component of the demodulation signal (hereinafter called the PM component). With regard to the latter, PM, component, by using the conventional time base corrector system, it is possible to negate the adverse effect, but with regard to the former, AM, component, no countermeasure has up to now been available.
FIG. 1 shows how modulation noise is caused by the jitter component. J.sub.0, +J.sub.1, +J.sub.2, -J.sub.1, -J.sub.2 represent a frequency spectrum of an FM carrier wave. For example, let the jitter component be a single frequency, f.sub.n ; then, it modulates according to the spectrum shown in FIG. 1A, and this appears and the J.sub.n component as modulation noise when demodulated. In FIG. 1, the hatched area represents the passing zone in demodulation. The existence of the f.sub.n component in this zone, by demodulation as the J.sub.n component, is the cause of inferior SN ratio in video reproduction quality.
Also, in the case of video recording and reproduction of the numerous Hadamard Transformer signals generated by the Hadamard Transformer System through a frequency modulation system, there is a channel which is especially easily affected by tape travel modulation noise. As is already known, in Hadamard Transformation, each channel has its own frequency band. Moreover, the transformer signal frequency is also different, and there is a channel which includes low frequency components such as direct current components.
Generally speaking, the frequency component of the modulation noise caused by tape travel is largely distributed in the region of a few Hertz to a few tens of Hertz. Therefore, where the noise component is mixed into reproduced demodulation signals of the low frequency channels, which includes direct current components, it is extremely difficult to seperate the modulation noise from the signal frequency, as the signal frequency and the modulation noise frequency are so similar.